We often want to have a look on the ongoing data traffic on RS485-Bus when developing and debugging new applications or when we determine faults in already running systems.
It's quite important to NOT connect an USB-RS485-Converter directly to the bus, as it has high influence through possibly connected 120R-Termination-Resistors or Pullup/Pulldown.
Therfore i soldered together a small PCB that is a Sniffer-Connector for RS485 busses with high impedance inputs. This should minimize the influence of sniffing parts and give you the ability to watch the bus as it may work without the debugging equipment.
Needed Parts:
-PCB
- Soldering stuff
- TL084P
- FTDI USB-RS485-Converter Cable
- some wires for bus connection
Following circuit is used:
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| Circuit of M3S-Analyzer-Snifferhardware |
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| Complete device |
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| Detail view |
Probably someone experienced trouble with influencing debugging equipment on RS485 busses as well, this may solve your problem ;)
